Orchids entice hornets with their prey's scent

Washington, Aug 7 (ANI): Scientists have found that a species of orchid attracts pollen-carrying hornets by wearing the scent of their prey.

Dendrobium sinense grows on the Chinese island of Hainan, where hornets capture honeybees to serve as food for their larvae.

It fools the hornets by producing a rare scent chemical that honeybees use to send an alarm.

The predatory insects recognise the smell and pounce on the flowers, only to find the larder empty. But they carry pollen with them to the next orchid that lures them into its honeybee trap.

"Of course, we are aware of the fascinating other examples of how orchids attract their pollinators. However, we did not expect to find such a new form of deception," said Manfred Ayasse of the University of Ulm in Germany.

Scientists already knew from previous studies that the hornet, Vespa bicolor, was a frequent visitor to D. sinense orchids.

Rather than landing and pausing on the petals, like most pollinators, the hornets instead swooped in on the red centre of the flower - as if attacking prey.

In the current study, they found that hornets were more apt to tackle orchids with their natural scent or dummy honeybees impregnated with the floral scent than they were odourless bee dummies.

An examination of the floral extract turned up Z-11-eicosen-1-ol as one of few compounds that might be detected by the antennae of worker hornets.

The chemical was known from other studies to be a major compound of honeybees' alarm pheromone and an essential component for prey recognition in hunting wasps.

Behavioral experiments of hornets in the lab confirmed the predatory insect's attraction to the orchid flower's scent and to Z-11-eicosen-1-ol alone.

People might take a note from these orchids about how to manipulate Vespa hornets to their own ends, according to the researchers.

"Various species of Vespa are problems to beekeepers, because they plunder the hives. Besides this, their ravages of fruit crops make hornets a serious pest to man. Our results could be used to develop environmentally responsible traps for pest hornets," Ayasse said.

The findings are published in the journal Current Biology. (ANI)